Approach Considerations

The results from hematologic and biochemical screening tests are normal. In some patients, an increase in blood histamine levels is seen after experimental scratching.

The diagnosis of dermographism is usually made by observing the clinical response after using moderate pressure to stroke or gently scratch the skin. The site is important because areas protected from regular pressure and environmental influences (eg, the back) typically are more reactive than more exposed areas (eg, the buttocks and limbs).

A dermographometer (spring-loaded stylus) can be used to apply graded, reproducible pressure (eg, 3600 g/cm2) and record skin responses. The use of this instrument is mostly limited to research settings.

Biopsy specimens show dermal edema with a few perivascular mononuclear cells.

Appearance of the word "Dermatographia" on a human arm 15 minutes after the letters have been traced with a blunt object on the skin. A type of urticaria or "hives", also known as dermatographic urticaria, dermatographism, or "skin writing".